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Abstract: This paper reports on the results of a numerical investigation designed toaddress how the initially anisotropic appearance of a GRB remnant is modifiedby the character of the circumburst medium and by the possible presence of anaccompanying supernova SN. Axisymmetric hydrodynamical calculations of light,impulsive jets propagating in both uniform and inhomogeneous external media arepresented, which show that the resulting dynamics of their remnants since theonset of the non-relativistic phase is different from the standard self-similarsolutions. Because massive star progenitors are expected to have their close-insurroundings modified by the progenitor winds, we consider both free winds andshocked winds as possible external media for GRB remnant evolution. Abundantconfirmation is provided here of the important notion that the morphology andvisibility of GRB remnants are determined largely by their circumstellarenvironments. For this reason, their detectability is highly biased in favor ofthose with massive star progenitors; although, in this class of models, thebeamed component may be difficult to identify because the GRB ejecta iseventually swept up by the accompanying SN. The number density of asymmetricGRB remnants in the local Universe could be, however, far larger if they expandin a tenuous interstellar medium, as expected for some short GRB progenitormodels. In these sources, the late size of the observable, asymmetric remnantcould extend over a wide, possibly resolvable angle and may be easier toconstrain directly.

Autor: Enrico Ramirez-Ruiz, Andrew I. MacFadyen


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